(1) Field of the Invention
The present invention relates to a TV channel selecting status monitoring method and apparatus and, more particularly, to a method and apparatus for determining a video/audio source and its broadcast channel to which the TV set is actually tuned.
(2) Description of the Prior Art
When a rating company monitors the channel tuning or selecting status of the TV set placed at each sample household for the purpose of audience measurement, a measuring apparatus called a TV sensor or audimeter is connected to the TV set so that the apparatus obtains TV set ON/OFF information and the number of the currently selected channel in association with time information and periodically sends them to a computer of the research center through a telephone circuit.
A source of video signals for display on the cathode-ray tube of the TV set and audio signals for output from its loudspeaker will hereinafter be referred to as a video/audio source, or simply as a source. A typical source is a VHF/UHF tuner built in the TV set. Other possible sources are a BS tuner, a CATV tuner, a CS (Communication Satellite) TV tuner, a VCR (Video Cassette Recorder), an electronic game machine, and so forth.
In the past when TV sets were usually used singly, it was necessary, for audience measurement, only to obtain the TV set ON/OFF information and the number of the channel actually selected by the VHF/UHF tuner in the TV set in association with time data. With the recent widespread use of a VCR and similar audio-visual (AV) apparatus and an AV/TV set (a TV set which has a plurality of video/audio input terminals and adapted to be used also as a monitor of an external apparatus such as a VCR), it has become necessary to detect the source actually selected by the TV set prior to the above-mentioned channel identification.
According to a conventional method (hereinafter referred to as a first conventional method) of searching for the actually selected source, audio signals to be applied from the VCR and similar sources to the TV set are each mixed with an identification signal of an inaudible frequency and are sequentially fed to individual video/audio input terminals, and a check is made to see if the identification signal is contained in each of audio signals obtained by picking up sounds from the loudspeaker of the TV set by a microphone. In this method, when the audio signal is decided as containing the identification signal, the video/audio input terminal corresponding thereto is specified as the video/audio input terminal currently selected for displaying video signals of the corresponding source on the TV set. Incidentally, when none of the video/audio input terminals are decided as being selected, it is determined that the broadcast waves are being received by the tuner in the TV set, if the TV set is ON and if the channel concerned can be specified.
On the other hand, there has been proposed a method (hereinafter referred to as a second conventional method) for detecting the channel on which video signals are actually displayed on the TV screen. This method detects a local oscillation signal of the tuner in the TV set to be monitored, and detects the currently receiving channel from the frequency of the oscillation signal through utilization of a one-to-one correspondence between them.
Another conventional method (hereinafter referred to as a third conventional method) is one that obtains an audio signal from the TV set and compares it with an audio signal of each channel played back by a reference receiver independently of the TV set, thereby identifying the currently selected by the TV set.
However, the first conventional method is applicable only to the TV set of the type that contains the VHF/UHF tuner alone, and is not applicable to TV sets of the type having incorporated therein one or more tuners as well as the VHF/UHF tuner, such as an AV/TV set containing a BS tuner and an AV/TV set containing a VCR built-in. The reason for this is, for example, that in the AV/TV set containing a BS tuner built-in, the BS broadcast wave bypasses video/audio input terminals and directly reaches the TV set. Accordingly, when no video/audio input terminals are selected, it is impossible to distinguish between the VHF/UHF and BS broadcasts although it is known that the actually selected source is either one of them. The same is true of the AV/TV set with a VCR built therein.
The second conventional method is applicable only to a TV set which receives analog broadcast waves alone, and is not suitable for application to a TV set which receives CS digital broadcast and like digital broadcasts as well. The CS digital broadcast digitizes video signals for data compression and transmits four to eight channels on a time-division multiplex basis through a single transponder. This makes it impossible to specify that one of the channels to which the tuner of the CS digital broadcast receiver is tuned, even if its channel selecting status is detected through utilization of the local oscillation frequency.
A third conventional method involves direct comparison of audio signals for the channel identification, and is applicable to such a digital broadcast as the CS digital broadcast as well as to the existing ground wave analog broadcast. With this method, however, it is often impossible to detect channels because there are cases where a silent period continues for a long time in TV programs.
A possible modification of the third conventional method is to use video signals in place of audio signals. That is, the video signal displayed on the TV screen is compared directly with the video signal on each of channels generated by reference receivers independently of the TV set; the channels selected by the reference receivers are changed until the both video signals coincide, and the channel for which the video signals coincide is specified as the channel currently selected. With this method, however, relatively much time is required for the comparison of video signals for each channel. Hence, the channel identification by the comparison of video signals for every channel inevitably consumes a large amount of time.
Moreover, the method by the direct comparison of video signals is based on the premise that the video signals for comparison can be generated in the monitoring apparatus independently of the TV set. Accordingly, in the CATV broadcast which uses video signals scrambled by suppression of sync signalsxe2x80x94recently widespread in urban areasxe2x80x94the video signals for comparison cannot be generated, and hence the channel identification is impossible. In the CATV broadcast, a pay channel is scrambled and a descramble signal is sent to contracted TV sets to descramble the video signals. However, the CATV receiver mounted in the monitoring apparatus is not formally contracted and hence is not supplied with the descramble signal; therefore, the video signals for comparison cannot be generated in the monitoring apparatus.
It is therefore an object of the present invention to provide a TV channel selecting status monitoring method and apparatus which permits detection of which source is being selected in a TV set which contains a plurality of sources such as a BS tuner and a VHF/UHF tuner and is also adapted for use as a monitor of an external source such as a CATV tuner.
Another object of the present invention is to provide a TV channel selecting status monitoring method and apparatus which, after the identification of a video/audio source actually selected by the user, permit efficient detection of that one of channels of video/audio source which is actually selected by the user.
Another object of the present invention is to provide a TV channel selecting status monitoring method and apparatus which, when candidate channels cannot be narrowed down to one particular channel actually selected by the user through the comparison of sync signals, permit ultimate detection of the actually selected channel by the comparison of video signals.
Still another object of the present invention is to provide a TV channel selecting status monitoring method and apparatus which permit the detection of an actually selected channel of the CATV broadcast as well by direct comparison of video signals.
According to a first aspect of the present invention, there is provided a TV channel selecting status monitoring method: for a TV set which has a plurality of video/audio sources built-in and at least one video/audio input terminal for inputting video and audio signals from at least one external video/audio source, said TV set being capable of providing a display and an acoustic output of -video and audio signals supplied from a user""s arbitrarily selected one of said video/audio sources, said method comprising the steps of: (a) detecting vertical and horizontal sync signals of a video signal applied to a cathode-ray tube of said TV set; (b) detecting video signals output from said plurality of video/audio sources built in said TV set; (c) detecting a video signal output from said video/audio source connected to said video/audio input terminal of said TV set; (d) sequentially selecting said video signals detected in said steps (b) and (c); (e) separating vertical and horizontal sync signals from each of said video signals sequentially selected in said step (d); (f) measuring the time difference between said vertical and horizontal sync signals detected in said step (a) and said vertical and horizontal sync signals selected in said step (e); and (g) correcting said time difference measured in said step (f) in accordance with a premeasured delay time inherent in each of said plurality of video/audio sources, and determining that that one of said video/audio sources for which said corrected time difference is minimum is the video/audio source currently selected by said user.
According to a second aspect of the present invention, there is provided a TV channel selecting status monitoring apparatus for a TV set which has a plurality of video/audio sources built-in and at least one video/audio input terminal for inputting video and audio signals from at least one external video/audio source, said TV set being capable of providing a display and an acoustic output of the video and audio signals supplied from a user""s arbitrarily selected one of said video/audio sources, said method comprising: sync signal detecting means for detecting vertical and horizontal sync signals of a video signal applied to a cathode-ray tube of said TV set; internal video signal detecting means for detecting video signals output from said plurality of video/audio sources built in said TV set; external video signal detecting means for detecting a video signal output from said video/audio source connected to said video/audio input terminal of said TV set; an analog switch which is supplied with said video signals detected by said internal video signal detecting means and said video signal detected by said external video signal detecting means, and selectively outputs one of said video signals; first sync separating means for separating vertical and horizontal sync signals from said video signal output from said analog switch; time difference measuring means which is supplied with first and second vertical and horizontal sync signals, and measures the time differences between said first and second vertical sync signals and between said first and second horizontal sync signals; and control means which: inputs said vertical and horizontal sync signals detected by said sync signal detecting means, as said first vertical and horizontal sync signals, to said time difference measuring means; inputs said vertical and horizontal sync signals separated by said first sync separating means from said video signal of each of said video/audio sources selectively fed thereto from said analog switch, as said second vertical and horizontal sync signals, to said time difference measuring means; measures, by said time difference measuring means, the time differences between said vertical and horizontal sync signals detected by said sync signal detecting means and said vertical and horizontal sync signals of said each video/audio source; corrects said measured time differences in accordance with a premeasured delay time inherent in said each video/audio source; and determines that one of said video/audio sources for which said corrected time difference is minimum is the video/audio source currently selected by said user.
According to a third aspect of the present invention, the method of the first aspect further comprises the steps of: (h) controlling a plurality of reference receivers to sequentially generate video signals of channels receivable from that one of said video/audio sources, which was determined to be currently selected by said user in said step (g), said plurality of reference receivers being capable of generating video signals of each channel of each TV broadcast independently of said TV set; (i) separating vertical and horizontal sync signals from each of said video signals generated in said step (h); (j) measuring the time difference between vertical and horizontal sync signals of said video/audio sources determined to be currently selected by said user in said step (g) and said vertical and horizontal sync signals separated in said step (i); and (k) correcting said time difference measured in said step (j) in accordance with a premeasured delay time inherent in each of said plurality of video/audio sources, and determining that a channel for which said corrected time difference is smaller than a predetermined threshold value is a candidate for a channel currently selected by said user.
According to a fourth aspect of the present invention, the apparatus of the second aspect further comprises: a plurality of reference receivers for generating video signals of each channel of each TV broadcast independently of said TV set; second sync separating means for separating vertical and horizontal sync signals from each of said video signals generated by said reference receivers; and a selector for selectively outputting either said vertical and horizontal sync signals detected by said sync signal detecting means or said vertical and horizontal sync signals separated by said second sync separating means; wherein said control means: inputs a video signal of said that one of video/audio source determined as being currently selected by said user, to said first sync separating means via said analog switch; inputs vertical and horizontal sync signals separated by said first sync separating means, as said first vertical and horizontal sync signals, to said time difference measuring means; sequentially generates, by said reference receivers, video ""signals of respective channels receivable from that one of said video/audio sources determined as currently selected by said user, and applies said video signals to said second sync separating means one by one; inputs vertical and horizontal sync signals separated by said second sync separating means, as said second vertical and horizontal sync signals, to said time difference measuring means; measures, by said time difference measuring means, the time differences between vertical and horizontal sync signals output from that one of said video/audio sources determined as currently selected by said user and vertical and horizontal sync signals of each channel generated by said reference receivers; corrects said measured time differences in accordance with a premeasured delay time inherent in said each of said plurality of video/audio sources; and determines that a channel for which said corrected time difference is smaller than a predetermined threshold value is a candidate for a channel currently selected by said user.
According to a fifth aspect of the present invention, the method of the third aspect further comprises the steps of: (l) when a plurality of channels are determined as candidates for said user""s currently selected channel in said step (k), controlling said plurality of reference receivers to sequentially generate video signals of the same channels as said candidate channels; and (m) comparing, at a plurality of sample points common thereto, a video signal generated from that one of said video/audio sources determined to be currently selected by said user in said step (g) and video signals sequentially generated in said step (l), and detecting said user""s currently selected channel based on the degree of coincidence between said video signals.
According to a sixth aspect of the present invention, the apparatus of the fifth aspect further comprises: a first A-D converter/frame memory for digitizing and storing said video signal output from said analog switch; and a second A-D converter/frame memory for digitizing and storing said video signals output from said reference receivers; wherein when a plurality of channels are determined as candidates for said user""s currently selected channel by the comparison of said sync signals, said control means: controls said plurality of reference receivers to sequentially generate video signals of the same channels as said candidate channels, and inputs said video signals to said second A-D converter/frame memory; stores in said first A-D converter/frame memory a video signal generated by that one of said video/audio sources determined as the source currently selected by said user; compares those video signals at a plurality of sample points common thereto; and detects said user""s currently selected channel based on the degree of coincidence between said video signals.
According to a seventh aspect of the present invention, the method of the fifth aspect further comprises the step of: (n) when said video/audio source connected to said video/audio input terminal of said TV set is a CATV tuner for CATV broadcast reception use, quasi-descrambling that one of video signals from a CATV receiver provided as said reference receiver which is of a pay channel scrambled by the suppression of sync signal; wherein said quasi-descrambling step (n) comprises the steps of: (n-1) generating vertical and horizontal blanking intervals from said vertical and horizontal sync signals detected in said step (a); (n-2) extracting signals in said vertical and horizontal blanking intervals in said scrambled video signal; (n-3) restoring said extracted signals to their original form before said video signal was scrambled; and (n-4) replacing said signals in said vertical and horizontal blanking intervals in said scrambled video signal with said restored signals to form descrambled video signals.
According to an eighth aspect of the present invention, the apparatus of the sixth aspect further comprises: a CATV receiver as one of said reference receivers; and a suppressed sync signal quasi-regenerator which quasi-descrambles that one of video signals from said CATV receiver which is of a pay channel scrambled by the suppression of sync signal; wherein said suppressed sync signal quasi-regenerator comprises: interval generating means for generating vertical and horizontal blanking intervals from said vertical and horizontal sync signals detected by said sync signal detecting means; signal extracting means for extracting signals in said vertical and horizontal blanking intervals in said scrambled video signal generated by said CATV receiver; sync signal restoring means for restoring said extracted signals to their original form before said video signal was scrambled; and video signal generating means for replacing said signals in said vertical and horizontal blanking intervals in said scrambled video signal from said CATV receiver with said restored signals from said sync signal restoring means to form descrambled video signals.
According to the first and second aspect of the present invention, vertical and horizontal sync signals are separated from video signals which are output from all selectable or receivable video/audio sources, that is, a plurality of video/audio sources built in the TV set and a plurality of video/audio sources disposed outside the TV set, and the phase differences between the vertical and horizontal sync signals of each of the video-audio source and vertical and horizontal sync signals of video signals applied to the cathode-ray tube of the TV set are measured. For at least a short time, the phase of the sync signal in the video signal from each video/audio source remains unchanged, and the phases of the sync signals from different video/audio sources are very unlikely to coincide. Accordingly, the video/audio source whose vertical and horizontal sync signals are in phase with those of the video signals applied to the cathode-ray tube can be decided as a source actually selected by the user.
According to the third and fourth aspects of the present invention, the phases of vertical and horizontal sync signals in the video signal from the video/audio source decided as being actually selected by the user are compared with the phases of vertical and horizontal sync signals of all receivable channels of the video/audio source decided as the actually selected source, generated by reference receivers independently of the TV set. For at least a short time, the phase of the sync signal in the video signal of each receivable channel of the video/audio source decided as being selected remains unchanged, and the phases of the sync signals from different channels are very unlikely to coincide. Hence, the channel actually selected can be identified by the comparison of sync signals in most cases. That is, that one of channels generated by the reference receivers independently of the TV set in which the vertical and horizontal sync signals coincide in phase with those in the video signal output from the video/audio source decided as being actually selected by the user can be decided as the actually selected channel.
According to the fifth and sixth aspects of the present invention, if the search for the actually selected channel by the comparison of sync signals fails to narrow down to one particular channel, the video signal from the video/audio source decided to be actually selected by the user is compared directly with :the video signal of each of the reference receivers corresponding to the channels narrowed down as candidates for the actually selected channel. Unlike the audio signal the video signal does not cease for a long time and the video signals on different channels are very unlikely to coincide. Hence, that one of channels generated by the reference receivers independently of the TV set in which the video signals coincide with those in the video signal output from the video/audio source decided as being actually selected by the user can be decided as the actually selected channel.
According to the seventh and eighth aspects of the present invention, when a video signal of the same channel as that of a scrambled video signal by the reference receiver is applied to the cathode-ray tube is fed to the cathode-ray tube of the TV set, vertical and horizontal sync signals of the video signal applied to the cathode-ray tube are used to quasi-descramble the reference video signal. Thus, the search for the actually selected channel by the direct calculation of video signals can also be made in the CATV broadcast using video signals scrambled by the suppression of sync signal.